This proposal requests funds for the acquisition of a cryoprobe for substantially increasing the sensitivity of the high-resolution 600 MHz NMR instrument in the WCAS Structural Biology NMR Facility at Northwestern University. With previous NIH and NSF support, Northwestern structural biologists established a resource for macromolecular NMR that has yielded significant results. The 600 MHz spectrometer, which is the only NMR instrument in the facility, is used heavily and continuously. The two- to three-fold increase in sensitivity afforded by cryoprobes over conventional third generation probes translates into four- to nine-fold reduction in acquisition times, thereby significantly enhancing throughput. The acquisition of a cryoprobe will thus more effectively meet the growing scientific needs of as many as six research groups that currently use the instrument. It also represents a cost-effective solution since the acquisition costs of a new 600 MHz instrument is significantly higher than that of a cryoprobe. An added benefit of the increased sensitivity of the cryoprobe is the lowered sample concentration requirements. Thus, studies of samples that are expensive to produce, prone to aggregate at high concentrations, or are otherwise chemically unstable are readily facilitated, thus opening up the possibility of studying research problems previously inaccessible by this technique. The cryoprobe we propose to acquire will have all the capabilities of third generation probes for macromolecular NMR including optimized direct detection of 1H frequencies, simultaneous irradiation at 1H, 2H, 13C, and 15N frequencies, and actively shielded z-axis gradient. Cryogenic cooling of the probe requires a closed-cycle cryogenic system comprising a helium refrigerator, a temperature controller, a helium compressor, and a turbo vacuum pump as well as a water chiller unit as essential accessories. The cryogenic system and the water chiller are fully compatible with and can be readily accommodated in the current layout of the NMR facility with only minor modifications to the facility. Approval of the site plan has been already obtained from the manufacturer. The cryoprobe along with the closed-cycle cryogenic system and water chiller as accessories will thus reestablish the 600 MHz instrument in the WCAS facility as a state-of-the-art resource for macromolecular NMR. [unreadable] [unreadable]